Abstract

The mixing unit attachment tab (LH) of a helicopter has failed by fatigue. Fractographic examination revealed two fatigue crack origins on the flat surface having the step. The fatigue cracks had initiated at corrosion pits. The pitting corrosion occurred due to presence of high concentration of chlorine (as high as 12.5 wt%). The source of chlorine needs to be identified and corrective measures incorporated to prevent recurrence of similar failures.